"[What are the[ effects of inactivation of endothelial nitric oxide synthase (eNOS) on cartilage development in mice?Skeletal growth and development of mice carrying a null mutation in the eNOS gene was studied in comparison to control littermates. In situ analyses were complemented by experiments with primary chondrocytes and tibial explants from these mice. eNOS-deficient mice show increased lethality and reduced bone growth, with hypocellular growth plates and a marked reduction in the number of proliferating chondrocytes. In vitro studies demonstrated lower chondrocyte numbers and reduced endochondral bone growth in mutants, suggesting that the role of eNOS signaling in chondrocyte proliferation is cell-autonomous[Meaning that the mutation is local per cell rather than system wide].Reduced chondrocyte numbers appear to be caused by decreased cyclin D1 and increased p57 expression in mutants, resulting in slower cell cycle progression and earlier cell cycle exit. In addition, expression of early chondrocyte markers such as Sox9 was reduced and prehypertrophic markers were expressed prematurely in mutant mice. eNOS [has a role] in chondrocyte proliferation and endochondral bone growth. Loss of eNOS results in premature cell-cycle exit and prehypertrophic chondrocyte differentiation during cartilage development.""NO is synthesized through l-arginine by NO synthases (NOS) in many cell types. Three different types of NOS have been identified. The neuronal NOS (nNOS or NOS1) and endothelial NOS (eNOS or NOS3) forms are constitutively expressed, and their activity is regulated by intracellular signaling and the calcium-binding protein calmodulin. The inducible form (iNOS or NOS2) is stimulated at the level of expression by factors including lipopolysaccharide and cytokines, such as interleukin-1, tumor necrosis factor α, and interferon-α, and leads to sustained and high levels of NO, mainly in inflammatory disease"

"NO signaling promotes chondrocyte hypertrophy"

"reduced numbers of cells in the proliferative zone are a general feature of eNOS−/− bones"

"the transcription factor ATF-3 is up-regulated during chondrocyte hypertrophy and represses the activity of the cyclin D1 promoter in chondrocytes. ATF-3 expression [increases] in eNOS-deficient growth plates, suggesting that premature induction of ATF-3 expression in mutant mice leads to repression of cyclin D1 transcription and chondrocyte proliferation."<-LSJL heavily upregulates ATF3.

"Both NO and CNP stimulate the production of cGMP via soluble or particulate guanylyl cyclases, these similarities provide further evidence of the importance of cGMP signaling in endochondral bone formation. However, the phenotype of eNOS-null mice does not exactly resemble that of mice lacking CNP or the main effector of cGMP in cartilage, cGMP-dependent kinase II. For example, mice lacking CNP have strikingly narrow growth plates and shorter proliferating and hypertrophic zones "These results are echoed by this study Reduced chondrocyte proliferation, earlier cell cycle exit and increased apoptosis in neuronal nitric oxide synthase-deficient mice. In this study chondrocytes with neurol nitric oxide deficiency, expressed more c-Fos, ATF3, and ROR-alpha(which inhibits chondrogenesis). Also, eNos and iNos levels were increased in nNOS KO mice. The study also noted that they did not notice the phenotype change of the a decrease in length of the hypertrophic zone which is typical in CNP null mice. The speculated that eNos and iNos may compensate for decreased nNos levels.

Now, Nitric Oxide appears to be only beneficial if you have sufficient quantities of the enzyme whereas exercise Nitric Oxide seems like it wouldn't have an additional effect. Perhaps increasing Cyclin D1 and decreasing p57 can result in supernatural growth. Nitric Oxide can be affected by exercise...

"Osteocytes are the major mechanosensor in bone, responsible for sending signals to the effector cells (osteoblasts and osteoclasts) that carry out bone formation and resorption. osteocytes release various soluble factors (e.g. transforming growth factor-beta, nitric oxide, and prostaglandins) that influence osteoblastic and osteoclastic{and possibly chondrocytes} activities when subjected to a variety of mechanical stimuli, including fluid flow[LSJL but we're more interested in the effects of chondrocytes but this might mean that direct loading of the spinous process of your vertebrae may increase your height], hydrostatic pressure, and mechanical stretching. Low-magnitude, high-frequency (LMHF) vibration (e.g., acceleration less than <1 x g, where g=9.81m/s(2), at 20-90 Hz) can positively influence skeletal homeostasis in animals and humans. Osteocytes are the mechanosensor responsible for detecting the vibration stimulation and producing soluble factors that modulate the activity of effector cells. We applied low-magnitude (0.3 x g) vibrations to osteocyte-like MLO-Y4 cells at various frequencies (30, 60, 90 Hz) for 1h. Osteocytes were sensitive to this vibration stimulus at the transcriptional level: COX-2 maximally increased by 344% at 90Hz, while RANKL decreased most significantly (-55%, p<0.01) at 60Hz[RANKL increases osteoclast activity]. Conditioned medium collected from the vibrated MLO-Y4 cells attenuated the formation of large osteoclasts (> or =10 nuclei) by 36% and the amount of osteoclastic resorption by 20%. The amount of soluble RANKL (sRANKL) in the conditioned medium was found to be 53% lower in the vibrated group, while PGE(2) release was also significantly decreased (-61%)."

"osteocytes have been found to communicate with effector cells through gap junctions and soluble factors"<-these soluble factors may promote chondrocyte differentiation as well.

"PGE2 released by bone cells has been found to increase upon fluid flow stimulation and mediate downstream responses such as increased expression of gap junction protein connexin (Cx) 43"

LMHF increased Cox2 but decreased PGE2.

Now, vibrations on the bone can be simulated by impact with exercises like jumping or tapping.

Nitric Oxide can only help in lengthening short, irregular, and flat bones as it affects osteoblasts and not chondrocytes(although there may be a yet unknown effect on chondrocytes). Nitric Oxide is one of the factors released by osteocytes in response to various mechanical strain. Nitric Oxide is affected by exercise as a result of fluid flow on the bone(lateral synovial joint loading which on non-long bones is any direction).

"chondrocyte-specific deletion of the gene Rac1 in mice leads to severe dwarfism due to reduced chondrocyte proliferation. Rac1-deficient chondrocytes have severely reduced levels of inducible nitric oxide synthase (iNOS) protein and nitric oxide (NO) production. NO donors reversed the proliferative effects induced by Rac1 deficiency, whereas inhibition of NO production mimicked the effects of Rac1 loss of function[so proper NO levels are essential to grow taller]. The growth plate of iNOS-deficient mice [have] reduced chondrocyte proliferation and expression of cyclin D1, resembling the phenotype of Rac1-deficient growth plates. Rac1-NO signaling inhibits the expression of ATF3, a known suppressor of cyclin D1 expression in chondrocytes[note that ATF3 is upregulated by LSJL so perhaps when performing LSJL NO signaling has to be enhanced to counteract the upregulation by LSJL]. "

"Chondrocytes in the hypertrophic zone of the growth plate undergo apoptosis during endochondral bone development via mechanisms that involve inorganic phosphate (Pi) and nitric oxide (NO){apoptosis may not necessarily be bad for height growth though}. Pi-dependent NO production plays a role in apoptosis of cells in the resting zone as well. Pi decreased the number of viable cells; the number of TUNEL-positive cells and the level of DNA fragmentation were increased, indicating an increase in apoptosis. Blocking NO production using the NO synthase (NOS) inhibitor L: -NAME or cells from eNOS(-/-) mice blocked Pi-induced chondrocyte apoptosis, indicating that NO production is necessary. NO donors NOC-18 and SNOG both induced chondrocyte apoptosis. SNOG also upregulated p53 expression, the Bax/Bcl-2 expression ratio, and cytochrome c release from mitochondria, as well as caspase-3 activity, indicating that NO induces apoptosis via a mitochondrial pathway. Inhibition of JNK, but not of p38 or ERK1/2, MAP kinase was able to block NO-induced apoptosis, indicating that JNK is necessary in this pathway. Pi elevates NO production via eNOS in resting zone chondrocytes, which leads to a mitochondrial apoptosis pathway dependent on JNK."

"Pi induced a concentration-dependent increase in caspase-3 activity, with 7.5 mM Pi causing a 3.4-fold increase compared with control culture"

"Pi regulated p53 abundance in resting zone chondrocytes. Although 2.5 mM Pi did not significantly increase p53, 5 and 7.5 mM Pi treatment increased p53 protein 2.6- and 2.8-fold, respectively. Pi also induced a concentration-dependent increase in levels of Bax and a concentration-dependent decrease in levels of Bcl-2. The Bax/Bcl-2 ratio was greatest in cultures treated with 7.5 mM exogenous Pi, with a sixfold increase compared to control."

Evaluation of methylation status of the eNOS promoter at birth in relation to childhood bone mineral content.

"eNOS is important in bone metabolism; we therefore related the methylation status of the eNOS gene promoter in stored umbilical cord to childhood bone size and density in a group of 9-year-old children. We assess the methylation status of two CpGs in the eNOS promoter in stored umbilical cords of 66 children who formed part of a Southampton birth cohort and who had measurements of bone size and density at age 9 years. Percentage methylation varied greatly between subjects. For one of the two CpGs, eNOS chr7:150315553 + , after taking account of age and sex, there were strong positive associations between methylation status and the child's whole-body bone area, bone mineral content, and areal bone mineral density at age 9 years. These associations were independent of previously documented maternal determinants of offspring bone mass. An association [exists] between methylation status at birth of a specific CpG within the eNOS promoter and bone mineral content in childhood. eNOS [has a role] in bone growth and metabolism."